The present invention relates to apparatus for detecting the position of an object within a viewing field. One anticipated use of the present invention is to detect the existence and location of a pointing object, such as a finger or pencil, on a computer display screen, such as a CRT screen. Another anticipated use is to detect the presence of a person in a confined area, such as a room.
In general, position detecting apparatus known in the art senses the interruption of radiation, such as light, by an opaque object, such as a part of the human body. This apparatus utilizes radiation transmitters, which transmit radiation across the viewing field, parallel to the viewing field surface, and radiation receivers which detect the radiation passed across the viewing field and sense the existance and location of any interruption in this radiation (e.g. by an object).
One type of conventional apparatus for detecting the light interruption position, in an X--Y plane, of a small object, such as a human finger or a pencil, utilizes an X-coordinate array of multiple light sources mounted along one side of a rectangular display panel and paired with a corresponding X-coordinate array of multiple light detectors mounted on the opposite side of the panel. Also, similar Y-coordinate arrays of paired multiple light sources and detectors are respectively mounted along the remaining two opposite sides of the rectangular panel. Thus, the perimeter of the panel is covered by oppositely paired arrays of light sources and detectors. Examples of such apparatus are disclosed in U.S. Pat. Nos. 3,478,220; 3,764,813; 3,775,560 and 3,860,754.
This type of detection apparatus has certain inherent disadvantages. First, spatial resolution of the apparatus is no better than the limitation imposed by the number, size and spacing of the individual light sources and detectors, one from the next in the respective arrays thereof. Thus, in some commercial equipment of this type, it is possible for the human finger to be placed between two adjacent detectors and be missed by the parallel beams of light provided by the sources. Second, the apparatus utilizes a large number of active elements, i.e. light sources and detectors, not counting the circuitry, which are costly and have to be precisely mounted, in most cases, by manual labor. Therefore, the component cost and cost of manufacture and assembly are high. Third, the excessive number of light sources and detectors necessitates complex and costly arrangements of circuit components to operate the apparatus.
Another type of interruption position detection apparatus is disclosed in the U.S. Pat. No. 4,144,449. This type of detection apparatus is comprised of a generally rectangular frame having four sides and an open interior for the work area or viewing field. Lamps are provided on the frame for continuously emitting light through the interior of the frame from three sides thereof. A pair of linear image detector devices are respectively mounted on the frame at the two corners thereof located on opposite ends of the fourth side. Apertures are also located at each of the two frame corners and between the detector devices and a frame interior for configuring coincident fields of light therefrom for the detector devices to view. Each of the detector devices is capable of receiving a respective field of light from the frame interior and sensing interruption of light at any location within this field. According to the U.S. Pat. No. 4,144,449, this detector apparatus has the advantage over the previously described apparatus having paired arrays of light sources and detectors in that the number of components is greatly reduced while the resolution of the apparatus is increased. In addition, the overall complexity and cost of the circuitry required to operate the detection apparatus disclosed in the U.S. Pat. No. 4,144,449 is reduced in comparison with that of the apparatus having paired arrays of light sources and detectors.
Nevertheless, the detection apparatus disclosed in the U.S. Pat. No. 4,144,449 requires a relatively large frame as well as elongate light sources arranged on at least three sides of this frame. Thus, even this type of detection apparatus is large and cumbersome and is not readily adapted to be retro-fitted onto an existing display screen.
Furthermore, this known detection apparatus is limited in its application to relatively small viewing areas such as computer display screens. It is not readily adaptable for detecting the position of an object within a large viewing field such as a room in a building. Although it is theoretically possible to arrange a linear light source around the walls of a room, such light source would be extremely expensive, subject to accidental damage and would be aesthetically unappealing.
It would be desirable to provide apparatus of the above described type for use in detecting the positions of objects in large as well as in small viewing fields. In the large viewing field application, the detection apparatus would be useful, for example, in room surveillance and security as well as in connection with mechanical robots. For example, the position detecting apparatus may be operative to effect an emergency power shutdown of a robot if a human being enters the robot's work area. Also, the apparatus may serve as a back-up system in detecting the robot's own position in case the robot becomes "confused" and does not know where it is.